Preparation of esters by aldehyde condensation



March 12, 1963 H. J. HAGEMEYER, JR, ET AL 3,081,344

PREPARATION OF ESTERS BY ALDEHYDE CONDENSATION Filed April 24, 1961 II [V $9 3m {Mm a 3 .5553 |l|| 3 2238 Al :93. .IIIII 5 N 2238 E828 a 255 60 1:93:52 l @255 3 1 5m mm QZEEE mm warmed W l.* IIII. .Zm N 586%. 528i .6331

INVENTORS ATTORNEYS United States Patent Office 3,081,344 Patented Mar. 12, 1963 3,081,344 PREPARATION OF ESTERS BY ALDEHYDE CONDENSATION Hugh J. Hagemeyer, Jr., and Howard N. Wright, In, Longview, Tex., assignors to Eastman Kodak Company, Rochester, N.Y., a corporation of New Jersey Filed Apr. 24, 1961, Ser. No. 105,033 6 Claims. (Cl. 260-494) This invention relates to the preparation of esters and more particularly to an improved method of producing aliphatic esters by the condensation of an u-monosubstituted aliphatic aldehyde.

The esters produced by our novel process are of the general formula, RCH CHRCO CH CHRCH R, wherein R is hydrogen or a lower alkyl group and R is a lower alkyl group. In our process such esters are obtained by the dimolecular condensation of an u-monosubstitute aliphatic aldehyde of 4 to 8 carbon atoms in the presence of an aluminum alkoxide catalyst.

The condensation of isobutyraldehyde in the presence of aluminum isobutyrate was reported by W. Tischtschenko, as abstracted in Chem. Zentr., 1906, 11, 1552-56. We have now developed an improved method for carrying out this type of condensation reaction.

Reactions that can occur when an aliphatic aldehyde is contacted with an aluminum alkoxide under condensation reaction conditions are represented by the following equations:

I 2ROEMJHCHO lEtOlElrO13C01(JH(\JI':ICH2R R R R (simple ester) 11 CHzR 2RCH2GHCHO RCHaCH-CH-iJOHO l. R a is (aldol) Ill CHaR RCHsCHCHO RCHrCH-CH QHO is is in I.

CHrR

1 RCHrCH-CH-C 01-12026 $HCH$R R OH R R (1, S-glycol-l-monoester) In the method of our invention we obtain a high yield of the simple ester of the formula,

as produced in reaction I, and reduced yields of other condensation products such as the aldol of reaction 11 and the 1,3-glycol-l-monoester of reaction III.

The method of our invention by which we obtain these novel results comprises, in general, continuously passing a stream 0 a dry, acid-free, u-monosubstituted aliphatic aldehyde of 4 to 8 carbon atoms in contact with an aluminum alkoxide through a reaction zone at a tem-' perature of 90 to 140 C., and preferably 115 to 130 C. The reaction zone effluent is continuously distilled at a temperature below 170 CplO separate the ester product than 100 ppm.

from the aluminum alkoxide without decomposing the latter. The aluminum alkoxide is recycled to the reaction zone.

The feed aldehyde for our process can be any a-mono- "substitutedaliphatic aldehyde of from 4 to 8 carbon atom including isobutyraldehyde, Z-methylbutyraldehyde, Z-ethylbutyraldehyde, Z-ethylhexanaldehyde, etc. The dimolecular condensation products'of the process are esters of the formula, RCH CHRCO CH CHR'CH R,

such as isobutyl isobutyrate, '2-methylbutyl 2-methy1- butyrate, Z-ethylbutyl Z-ethylbutyrate, 2-ethylhexyl 2- ethylhexoate, etc.

The use of an aluminum alkoxide catalyst is an essen tial element of our process. A more basic catalyst such as magnesium alkoxide results in an excessive formation of aldol or of glycol monoester by reactions II and III above. The aluminum alkoxide catalyst is prepared by reacting aluminum metal with an aliphatic alcohol. In general, any aliphatic alcohol having no more than about 8 carbon atoms can be employed but aluminum alkoxides of the primary aliphatic alcohols of 4 to 8 carbon atoms catalyze the aldehyde condensation reaction better than those of the lower alcohols or the secondary alcohols. Preferably, we employ the alcohol derived from the feed aldehyde in order to prevent ester interchange when the aluminum alkoxide is in contact with the ester product.

The aluminum metal and alcohol react in the ratio of one mole of aluminum to 3 moles of alcohol but preferably an excess, e.g. 10% molar excess, of the dry alcohol is employed. The reaction is preferably catalyzed with a halogeuic activator such as aluminum chloride, mercuric chloride, iodine or carbon tetrachloride.

In the process of our invention the condensation reaction is carried out under substantially, anhydrous conditions and in an acid-free medium. Accordingly, the catalyst is also prepared under substantially anhydrous and acid-free conditions. In forming the catalyst the alcohol should contain less than 100 parts by weight per million parts of alcohol (hereinafter abbreviated as ppm.) of water and acid. When the reaction between the alcohol and the aluminum is complete the aluminum alkoxide is dissolved in enough dry aliphatic ester, i.e. a portion of the desired ester product, to form a convenient catalyst solution, e.g., S to 25 weight percent catalyst. Except for the ester itself that is used as the catalyst solvent, no solvent is used in our process. In fact, the use of a solvent will reduce the rate of reaction by dilution and is therefore to be avoided.

Our novel process will be described in more detail by reference to the drawing, the sole FIGURE of which is a schematic flow diagram of a preferred embodiment of the process.

The catalyst solution, e.g., a 10% solution of aluminum isobutoxide in isobutyl isobutyrate, is supplied from a catalyst tank 10 via lines 11 and 12 to the reactor 14. The aliphatic aldehyde, e.g. isobutyraldehyde, is supplied from an aldehyde feed tank 16 via line 17 to the drying column 18. Distillation in column 18 is carried out under conditions adapted to reduce the water content of the aldehyde to less than 20 p.p.m., and preferably to less than 10 p.p.m., and to reduce the acid content to less The aldehyde is withdrawn as a side stream from column 18 via line 20, thus being separated from the water taken overhead by line 21 and the acid and higher boiling impurities removed as a bottoms sludge by line 22. The dry, acid-free aldehyde stream is continuously fed to the reactor 14 by line 23 where it mingles with the catalyst introduced by line 12.

Reactor vessel 14 preferably is provided with means for agitating the reaction mass, such as a mechanical stirrer or a circulating pump, and with means for heating or cooling the reactor, such as a heating or cooling jacket surrounding the vessel or a coil within the vessel, not shown in the schematic flow diagram. The reactor is blanketed with a dry, inert atmosphere such as nitrogen or methane. The reactor temperature is maintained at -l40 C. and preferably at l15-130 C. The reactor is maintained approximately at atmospheric pressure although somewhat higher or lower pressure can be used. The feed rate of aluminum alkoxide catalyst to the reactor is selected in accordance with the aldehyde feed rate to provide a catalyst concentration in the range of 0.5

to 4.0 weight percent based on the aldehyde. The feed rate of the aldehyde is selected to provide a residence or longer residence time is permissible.

.The reactor temperature can be controlled by external heating or cooling or by controlling the feed rate of the aldehyde or catalyst. We prefer to employ constant feed est catalyst life when the aldehyde feed is dried to an extent such that the reaction feeds contain less than p.p.m. of water.

We have described the purification of the aldehyde feed by distillation. This is the preferred method for reducing both the water and acid content of the aldehyde to the indicated low levels.

Reactor temperature was maintained at about 120 C. by the use of mercury pressure, pressure. The redistilled isobutyl isobutyrate contained less than 1 percent impurities. Yield of isobutyraldehyde to ester was 97.9 percent and to glycol ester 2.1 percent.

The next two examples demonstrate the use of a temperature below the range used in our process.

isobutoxide catalyst that had been used in three previous runs, such as described in Example 1, was fed continuous- 2.0 weight percent aluminum isobutoxide in Reactor temperature was maintained at 70 Reactor cent isobutanol, 81 percent isobutyl isobutyrate and 15 The yield of isobutyraldehyde to isobutyl isobutyrate was 83.7 percent. eactor crude product was purified as in Eaxample 1.

was 1.2 hours. as in Example I.

The next example demonstrates a large scale operation of our new process.

Example 4 Isobutyraldehyde containing less than 5 p and less than 0.01 ercent isobutyric acid was fed into a gallon capacity circulated reactor at 2300 pounds per day. The catalyst solution was fed continuously at the rate to maintain 0.6 weight percent aluminum isobutoxide in the reactor. The reactor temperature was maintained between and 116 C. by external heating. The reactor crude product contained 3 to 5 percent isobutyl isobutyrate and 6 to 11 percent glycol ester. actor residence time was four hours. The crude reactor limits.

- action zone effluent at a temperature product was purified in a continuous distillation system, as in Example 1.

The next two examples demonstrate the use of different aldehyde feeds and the reaction of suchaldehydes at low temperature and subsequently at temperature within the scope of our process.

Example Example 6 When Z-ethylbutyraldehyde was reacted by the method of Example 5 at a temperature below 70 C., the conversion to the 12-carbon ester, Z-ethylbutyl Z-ethylbutyrate, was 65 percent. The reaction was carried out at 125 C.

*and the conversion to the ester was 88 percent.

As demonstrated by the above working examples, our use of a reaction temperature substantially higher than has previously been considered suitable for such aldehyde condensation reaction, i.e. 90 to 140 C. and preferably 115 to 130 C., 'n combination with the other elements of our process results in an unexpected improvement in the yield of the desired simple ester and a reduced or negligible yield of products such as the glycol monoester and the aldol.- By carrying out the reaction with continuous flow of feed, catalyst and product streams, we are able to control the feed rates (and thus the catalystaldehyde ratio and the residence time), the reactor temperature and'the drying column operation within narrow Thus we achieve the benefits of the novel combination of reaction conditions that characterize our process. Also by using a continuous flow system, in contrast to a batch-type reaction, we maintain a low concentration of free aldehyde in the reaction zone. This aids in maintaining the required reaction temperature and substantially eliminating reactions II and III indicated above.

Furthermore, our use of anhydrous and acid-free reactants and catalyst and low-temperature (i.e. below 170 C.) distillation of the crude product prevent decomposition of the aluminum alkoxide catalyst and make it possible to recycle the catalyst to the reaction zone, essentially free of aluminum hydroxide that would promote formation of the undesired glycol ester.

We have thus provided an improved method for obtaining the simple aliphatic ester dimolecular condensation product. Most importantly the new method provides a high yield of the desired simple aliphatic ester with a minimum amount of undesired by-products.

Although the invention has been described in considerable detail with reference to certain preferred embodiments thereof, it will be understood that variations and modifications can be effected within the spirit and scope of the invention as described hereinabove and as defined in the appended claims.

We claim:

' l. The process which comprises continuously passing a stream of a-monosubstituted aliphatic aldehyde of from 4 to 8 carbon atoms in contact with an aluminum alkoxide catalyst through a reaction zone at a temperature of 90 to 140 C., said aldehyde and said aluminum alkoxide having such a low content of water and acid that the mixture of aldehyde and aluminum alkoxide fed to the reaction zone contains less than 20 p.p.m. of water and less than 100 p.p.m. of acid, continuously distilling the rebelow 170 C. to separate the aluminum alkoxide from the ester product, and recycling aluminum alkoxide to the reaction zone.

2. The process which comprises drying to a water content less than 10 ppm. a C -C aldehyde of the formula, RCH CHRCHO, wherein R is selected from the group consisting of hydrogen and lower all: 1 groups and R is a lower alkyl group, and reducing the acid content of the aldehyde to less than p.p.m., continuously passing a stream of said aldehyde through a reaction zone in contact with a stream of a substantially dry and acid-free solution of an aluminum alkoxide catalyst prepared from the alcohol derived from said aldehyde, the mixture of aldehyde and catalyst fed to the reaction zone having a water content less than 10 p.p.m. and an acid content less than 100 p.p.m., said reaction zone being maintained at a temperature of to C., continuously distilling the reaction zone effiuent at a temperature below C. to separate undecomposed aluminum alkoxide catalyst from an ester product of the formula,

and recycling said catalyst to the reaction zone.

3. The process for preparing an ester of the formula, RCH CHR'CO CH CHRCH R, wherein R is selected from the group consisting of hydrogen and lower alkyl groups and R is a lower alkyl group, which comprises distilling a stream of a C C aldehyde of the formula, RCH CHR'CHO, and reducing its water content to less than 10 p.p.m. and its acid content to less than 100 p.p.m., forming a catalyst solution of an aluminum alkoxide and said ester, said aluminum alkoixde being prepared from the alcohol derived from said aldehyde and having a. water content of less than 100 p.p.m. and an acid content of less than 100 p.p.m., continuously passing a stream of said aldehyde in contact with a stream of said catalyst solution through a reaction zone at atmospheric pressure and a temperature of 115 to 130 C., the flow rate of said aldehyde and catalyst streams being such that the concentration of catalyst in the reaction zone is from 0.5 to 4.0 weight percent based on the aldehyde and the residence time within the reaction zone is about 0.5 to 2 hours, vacuum distilling the reaction zone effluent at a temperature below 170 C. to separate undecomposed aluminum alkoxide from said ester reaction product and recycling said catalyst to the reaction zone.

4. The process which comprises distilling a stream of isobutyraldehyde and reducing its water content to less than 10 p.p.m. and its acid content to less than 100 p p.rn., forming a catalyst solution of about 5 to 25% aluminum isobutoxide in isobutyl isobutyrate having a water content of less than 10 p.p.m. and an acid content of less than 100 p.p.m., continuously passing a stream of said isooutyraldehyde through a reaction zone in contact with a stream of said catalyst solution at a temperature of 115- 130 C., the flow rates of the aldehyde and catalyst streams being such that the concentration of catalyst in the reaction zone is from 0.5 to 4.0 weight percent based on the aldehyde and the residence time within the reaction zone 'is about one hour, vacuum distilling the reaction zone efiluent at a temperature below 170 C. to separate undecomposed aluminum isobutoxide catalyst from the isobutyl isobutyrate reaction product and recycling said catalyst to the reaction zone.

5. The process which comprises distilling a stream of Z-methylbutyraldehyde and reducing its water content to less than 10 p.p.m. and its acid content to less than 100 p.p.m., forming a catalyst solution of about 5 to 25% aluminum amyloxide in Z-methylbutyl Z-methylbutyrate having a water content of less than 10 p.p.m. and an acid content of less than 100 p.p.m., continuously passing a stream of said Z-methylbutyraldehyde through a reaction zone in contact with a stream of said catalyst solution at a temperature of 115-130 C., the flow rates of the aldehyde and catalyst streams being such that the concentration of catalyst in the reaction zone is from 0.5 to 4.0 percent based on the aldehyde and the residence time within the reaction is about one hour, vacuum distilling the reaction zone efliuent at a temperature below 170 C.

7 a? to separate undecomposed aluminum amyloxide catalyst um distilling the reaction zone eflluent at a temperature from the Z-methylbutyl Z-methylbutyrate reaction product below 170 C. to separate undeeomposed aluminum 2- and recycling said catalyst to the reaction zone. ethylbutoxide catalyst from the Z-cthylbutyl Z-ethyl- The process which comprises distilling a stream of hutyrate reaction product and recycling said catalyst to Z-ethylbutyraldehyde and reducing its Water content to 5 the reaction zone. less than p.p.m. and its acid content to less than 100 p.p.m., forming a catalyst solution of about 5 to References Cited in the file of this patent Zlurninum 2t-ethylbiitoiticlielin iZt-lethyigutyl Z-ethybutyratg UNITED STATES PATENTS aving a Wa er con en 0 ess ran p.p.m. an an act content of less than p.p.m., continuously passing a 10 1642689 Mudgan a p 8 3 stream of said Z-ethylbutyraldehyde through a reaction 2,412,463 f cl zone in contact with a stream of said catalyst solution at culson et 1 U56 a temperature of -130 C., the flow rates of the alde- OTHER REFERENCES Kulpinslti et al.: Journal of Organic Chemistry." vol. is from 0.5 to 4.0 15 8 pp 256470 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3381,3441 March 12, 1963 Hugh J. Hagemeyer, Jr. et a1.

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 6, line 28, for "alkoixde" read alkoxide line 30, for "100" read l0 Signed and sealed this 22nd day of October 1963.

(SEAL) Attest:

EDWIN L. REYNO DS ERNEST W. SWIDER L Attesting Officer Ac ting Commissioner of Patents 

1. THE PROCESS WHICH COMPRISES CONTINUOUSLY PASSING A STREAM OF A-MONOSUBSTITUTED ALIPHATIC ALDEHYDE OF FROM 4 TO 8 CARBON ATOMS ON CONTACT WITH AN ALUMINUM ALKOXIDE CATALYST THROUGH A REACTION ZONE AT A TEMEPERATIRE OF 90 TO 140* C., SAID ALDEHYDE AND SAID ALUMINUM ALKOXIDE HAVING SUCH A LOW CONTENT OF WATER AND ACID THAT THE MIXTURE OF ALDEHYDE AND ALUMINUM ALKOXIDE FED TO THE REACTION ZONE CONTAINS LESS THAN 20 P.P.M. OF WATER AND LESS THAN 100 P.P.M. OF ACID, CONTINUOUSLY DISTILLING THE REACTION ZONE EFFLUENT AT A TEMPERATURE BELOW 170* C. TO SEPARATE THE ALUMINUM ALKOXIDE FROM THE ESTER PRODUCT, AND RECYCLING ALUMINUM ALKOXIDE TO THE REACTION ZONE. 